INFLUENCE OF GLYPHOSATE ON RHIZOCTONIA ROOT-ROT, GROWTH, AND YIELD OF BARLEY

Time intervals between applying glyphosate to kill volunteer cereals and weeds and planting spring barley by direct drilling (no-till) into Rhizoctonia-infested soil were evaluated in field plots at Pendleton, Oregon, and Lacrosse and Lind, Washington. As the interval was shortened from autumn to spring application or from 3 wk to 3 days before planting in the spring, severity of Rhizoctonia root rot increased and grain yield decreased. When glyphosate applications were delayed until 2 or 3 days before planting (commonly used in production of spring barley in the Pacific Northwest), spring barley yields were reduced as much as 50% compared to when glyphosate was applied in the autumn or early spring. Disease was not as prevalent when glyphosate was applied 1 or 2 days after direct drilling compared with applications made 3 days before planting. Rhizoctonia root rot was least on spring barley when tillage or application of glyphosate was performed in the autumn or in spring 3 wk before planting. Tilling soil 2 days before planting at one site nullified the yield-depressing effect of a preplant glyphosate application. These results suggest that the inoculum potential for R. solani AG-8 as a pathogen of spring barley is strongly influenced by the timing of volunteer cereal and weed elimination and that adjustments in such practices can minimize crop damage and maximize yield.